The lighter three Group 5 elements occur naturally and share similar properties; all three are hard refractory metals under standard conditions. The fourth element, dubnium, has been synthesized in laboratories, but it has not been found occurring in nature, with half-life of the most stable isotope, dubnium-268, being only 29 hours, and other isotopes even more radioactive. To date, no experiments in a supercollider have been conducted to synthesize the next member of the group, either unpentpentium (Upp) or unpentseptium (Ups). As unpentpentium and unpentseptium are both late period 8 elements it is unlikely that these elements will be synthesized in the near future.

Most of the chemistry has been observed only for the first three members of the group, the chemistry of dubnium is not very established and therefore the rest of the section deals only with vanadium, niobium, and tantalum. All the elements of the group are reactive metals with a high melting points (1910 °C, 2477 °C, 3017 °C). The reactivity is not always obvious due to the rapid formation of a stable oxide layer, which prevents further reactions, similarly to trends in Group 3 or Group 4. The metals form different oxides: vanadium forms vanadium(II) oxide, vanadium(III) oxide, vanadium(IV) oxide and vanadium(V) oxide, niobium forms niobium(II) oxide, niobium(IV) oxide and niobium(V) oxide, but out of tantalum oxides only tantalum(V) oxide is characterized. Metal(V) oxides are generally nonreactive and act like acids rather than bases, but the lower oxides are less stable. They, however, have some unusual properties for oxides, such as high electric conductivity.[1]

All three elements form various inorganic compounds, generally in the oxidation state of +5. Lower oxidation states are also known, but they are less stable, decreasing in stability with atomic mass increase.

History

Vanadium was discovered by Andrés Manuel del Río, a Spanish-born Mexican mineralogist, in 1801 in the mineral vanadinite. After other chemists rejected his discovery of erythronium he retracted his claim.[2]

Tantalum was first discovered in 1802 by Anders Gustav Ekeberg. However, it was thought to be identical to niobium until 1846, when Heinrich Rose proved that the two elements were different. Pure tantalum was not produced until 1903.[4]

Occurrence

There are 160 parts per million of vanadium in the earth's crust, making it the 19th most abundant element there. Soil contains on average 100 parts per million of vanadium, and seawater contains 1.5 parts per billion of vanadium. A typical human contains 285 parts per billion of vanadium. Over 60 vanadium ores are known, including vanadinite, patronite, and carnotite.[4]

There are 20 parts per million of niobium in the earth's crust, making it the 33rd most abundant element there. Soil contains on average 24 parts per million of niobium, and seawater contains 900 parts per quadrillion of niobium. A typical human contains 21 parts per billion of niobium. Niobium is in the minerals columbite and pyrochlore.[4]

There are 2 parts per million of tantalum in the earth's crust, making it the 51st most abundant element there. Soil contains on average 1 to 2 parts per billion of tantalum, and seawater contains 2 parts per trillion of tantalum. A typical human contains 2.9 parts per billion of tantalum. Tantalum is found in the minerals tantalite and pyrochlore.[4]

Production

Approximately 70000 metric tons of vanadium ore are produced yearly, with 25000 metric tons of vanadium ore being produced in Russia, 24000 in South Africa, 19000 in China, and 1000 in Kazakhstan. 7000 metric tons of vanadium metal are produced each year. It is impossible to obtain vanadium by heating its ore with carbon. Instead, vanadium is produced by heating vanadium oxide with calcium in a pressure vessel. Very high-purity vanadium is produced from a reaction of vanadium trichloride with magnesium.[4]

70000 metric tons of tantalum ore are produced yearly. Brazil produces 90% of tantalum ore, with Canada, Australia, China, and Rwanda also producing the element. The demand for tantalum is around 1200 metric tons per year.[4]

Dubnium is produced synthetically by bombarding actinides with lighter elements.[4]

Biological occurrences

Out of the group 5 elements, only vanadium has been identified as playing a role in the biological chemistry of living systems, but even it plays a very limited role in biology, and is more important in ocean environments than on land.

Vanadium, essential to ascidians and tunicates as vanabins, has been known in the blood cells of Ascidiacea (sea squirts) since 1911[5] in concentrations of vanadium in their blood more than 100 times higher than the concentration of vanadium in the seawater around them. Several species of macrofungi accumulate vanadium (up to 500 mg/kg in dry weight).[6] Vanadium-dependent bromoperoxidase generates organobromine compounds in a number of species of marine algae.[7]

Rats and chickens are also known to require vanadium in very small amounts and deficiencies result in reduced growth and impaired reproduction.[8] Vanadium is a relatively controversial dietary supplement, primarily for increasing insulin sensitivity[9] and body-building. Vanadyl sulfate may improve glucose control in people with type 2 diabetes.[10] In addition, decavanadate and oxovanadates are species that potentially have many biological activities and that have been successfully used as tools in the comprehension of several biochemical processes.[11]